A duplex steel liner plate for a semi-autogenous mill and a method of manufacturing the same

Abstract

The application belongs to the technical field of metal wear-resistant materials, and particularly relates to a wear-resistant alloy dual-phase steel lining plate for a semi-autogenous mill and a manufacturing method thereof, the manufacturing method comprising molding, smelting, casting and magnetic field assisted targeted heat treatment. The application guarantees uniform proportion of bainite-martensite dual phase by optimizing alloy components, matching air cooling + fog cooling precise temperature control phase change window; the application maximizes purification and refining effect by using rare earth cored wire wire feeding to inhibit burning loss and promote uniform distribution; the application uses strong magnetic field to promote nucleation and weak magnetic field to guide growth, and manufactures dual-phase structure steel lining plate with 45%-55% lath bainite, 40%-50% acicular martensite and 3%-5% residual austenite, the hardness of which reaches HRC50-55, the tensile strength is 1520-1530 MPa, the impact toughness is good, the wear rate is low, the interface bonding strength is greater than or equal to 850 MPa, and the dual-phase structure steel lining plate has high reliability and durability in high stress and high wear environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal wear-resistant materials, and particularly relates to a wear-resistant alloy dual-phase steel lining plate for a semi-autogenous mill and a manufacturing method thereof. BACKGROUND

[0002] The semi-autogenous mill is a kind of grinding equipment widely used in the mining, cement, chemical and other industries. In the working process of the semi-autogenous mill, the internal ore and steel balls will produce strong impact, wear and corrosion on the mill cylinder. The ordinary cylinder material is difficult to withstand such harsh working environment, and is prone to wear, deformation and even damage, resulting in the mill unable to operate normally. The lining plate can be installed on the inner wall of the mill cylinder to protect the cylinder. At the same time, the lining plate designed and manufactured reasonably can optimize the movement trajectory of the grinding medium, enhance the grinding effect, and improve the production capacity and product quality of the mill. Therefore, in order to improve the overall performance of the semi-autogenous mill, a suitable lining plate needs to be made.

[0003] At present, the service life of the semi-autogenous mill lining plate on the market is basically 3-5 months, and the cylinder needs to be frequently replaced, which not only increases the purchase cost of the equipment, but also causes production interruption due to equipment downtime for maintenance, resulting in huge economic losses. The production of durable and efficient lining plates can prolong the service life of the lining plates, reduce the replacement frequency, reduce the equipment maintenance cost and downtime, and thus improve the economic benefits of enterprises.

[0004] Martensite can significantly improve the wear resistance of the material due to its extremely high hardness and strength. Although the hardness of bainite is slightly lower than that of martensite, bainite still has high strength. At the same time, the high toughness of bainite can effectively absorb impact energy and prevent crack propagation. This high toughness enables the material to exhibit excellent crack resistance under high stress and impact load. By reasonably controlling the proportion of bainite and martensite, the balance between hardness and toughness can be achieved, so that the material exhibits excellent comprehensive performance under complex working conditions. In recent years, bainite-martensite dual-phase steel has become a research hotspot. However, the existing technology still has the following problems:

[0005] The traditional process controls bainite transformation through a single cooling rate, which is difficult to accurately match the requirements of the "nucleation-growth" two-stage process, resulting in low aspect ratio and poor parallel arrangement of lath-shaped bainite, and limited impact resistance. The interface bonding strength between bainite and martensite is insufficient, and cracks are easily formed under impact load, leading to early failure of the lining plate. During quenching, the cooling rate of different parts of the workpiece is greatly different, resulting in uneven microstructure. Moreover, there is a lack of active control means for atomic diffusion, and carbides are randomly precipitated between bainite laths, weakening the interlath bonding force. The existing technology prolongs the bainite transformation window by increasing the content of Cr and Mo (>3%), but this increases the cost and easily leads to coarse as-cast structure. SUMMARY

[0006] The present application aims at solving the problems existing in the prior art and provides a wear-resistant alloy dual-phase steel lining plate for a semi-autogenous mill and a manufacturing method thereof.

[0007] To achieve the above object, the present application adopts the following technical scheme:

[0008] The present application provides a wear-resistant alloy dual-phase steel lining plate for a semi-autogenous mill, which comprises the following chemical components in percentage by mass: C: 0.35%-0.5%, Si: 0.8%-1.2%, Mn: 0.2%-0.6%, Cr: 1.8%-2.5%, Mo: 0.2%-0.6%, Cu: 0.3%-0.6%, RE: 0.2%-0.4%, Ti: 0.03%-0.05%, Nb: 0.02%-0.03%, B: 0.002%-0.005%, and the balance of Fe and inevitable impurities.

[0009] The microstructure of the wear-resistant alloy dual-phase steel lining plate for a semi-autogenous mill consists of 45%-55% lath-shaped bainite, 40%-50% acicular martensite and 3%-5% residual austenite; the lath-shaped bainite has a length-diameter ratio of ≥15:1 and a parallel arrangement degree of ≥85%.

[0010] The functions and selection of each element are as follows:

[0011] C: Carbon is the most basic strengthening element in steel, which can improve the hardness and strength of the steel. However, too high carbon content will reduce the toughness of the steel, and the carbon content in the present application is controlled at 0.35%-0.5% to balance the hardness and toughness.

[0012] Si: Silicon can solid solution strengthen ferrite, improve the strength and hardness of the steel, and inhibit the precipitation of carbides during bainite transformation, and promote the formation of lath-shaped bainite. However, too high silicon content will lead to the decline of the welding performance of the steel, so it is controlled at 0.8%-1.2%.

[0013] Mn: Manganese can improve the hardenability of the steel and promote the formation of bainite and martensite. However, too high manganese content will lead to the grain coarsening of the steel and reduce the toughness, so it is controlled at 0.2%-0.6%.

[0014] Cr: Chromium can significantly improve the hardenability and wear resistance of the steel, and delay the formation of pearlite during bainite transformation, and expand the bainite transformation zone. The chromium content in the present application is controlled at 1.8%-2.5%, which cooperates with the magnetic field to prolong the bainite transformation time and inhibit the generation of pearlite.

[0015] Mo: Molybdenum can further improve the hardenability of the steel, refine the grain, and reduce the bainite nucleation activation energy. Under the action of the magnetic field, the effect of molybdenum is more significant, which can further reduce the bainite nucleation activation energy by 15%. If the content of molybdenum is too high, the cost will increase, so the content is controlled within 0.2%-0.6%.

[0016] Cu: Strengthen ferrite, do not form carbide, expand y zone; improve corrosion resistance (including gas corrosion resistance); move the austenite isothermal transformation diagram to the right, improve the hardenability; reduce the Ms point; do not change the temper brittleness, and the content is controlled within 0.3%-0.6%.

[0017] RE (rare earth): Rare earth elements can purify grain boundaries, refine grains, improve toughness and fatigue resistance of the steel. The present application adopts La and Ce composite rare earth (La: Ce = 2: 1), and the content is controlled within 0.2%-0.4%. Under the action of the magnetic field, the segregation effect of rare earth on the grain boundary is enhanced (the concentration is increased by 40%), and the austenite grain is further refined to ≤30 μm, which provides more grain boundary nucleation sites for the directional growth of bainite laths.

[0018] Ti, Nb: Titanium and niobium can form fine carbonitride, prevent austenite grains from growing at high temperature, refine grains, and improve the strength and toughness of the steel. The content of titanium is controlled within 0.03%-0.05%, and the content of niobium is controlled within 0.02%-0.03%.

[0019] B: Boron can significantly improve the hardenability of the steel, and a small amount of boron (0.002%-0.005%) can segregate at the grain boundary, reduce the bainite nucleation work, and promote the bainite nucleation. Under the action of the magnetic field, the distribution of boron is more uniform (the segregation degree is ≤10%), which further improves the bainite nucleation density.

[0020] The present application also provides a manufacturing method of the aforementioned semi-autogenous mill wear-resistant alloy dual-phase steel lining plate, which specifically comprises the following steps:

[0021] (1) Modeling: V-method molding process is adopted, 0.12-0.15 mm thick polyethylene film is used, and the neck diameter of the riser is 1.3-1.6 times the wall thickness of the casting.

[0022] The vacuum sealing principle is used, the plastic film covering the sand box is tightly attached to the sand grains through vacuum pumping, and a compact sand mold is formed. The polyethylene film plays the role of isolation and sealing, the riser generates heat during pouring, compensates the volume shrinkage of the casting, and prevents defects such as shrinkage holes and shrinkage porosity. The neck diameter of the riser is 1.3-1.6 times the wall thickness of the casting, which is to ensure that the riser can effectively supplement the casting. If the neck diameter of the riser is too small, the supplementing ability is insufficient; if it is too large, the volume of the riser will increase, which will waste materials and is not conducive to operation.

[0023] (2) Melting: the intermediate frequency furnace is heated to 1660-1680 °C, and pig iron, scrap steel and alloy materials are added for melting; 1600-1620 °C, add composite purifying agent; then use silicon iron pre-deoxidation and aluminum wire final deoxidation, stir for 15 minutes, then remove the slag, control the oxygen content ≤12ppm, control the sulfur content ≤0.008%; then stop heating, the furnace is cooled to 1520-1550 °C, rare earth cored wire and Ti-Nb-B composite compression block are added, argon blowing stirring: 1.0-1.2 m 3 / h, ≥10 minutes;

[0024] The intermediate frequency furnace quickly melts the pig iron, scrap steel and alloy materials by induction heating to reach the required melting temperature; the composite purifying agent reacts with the impurities in the molten steel at high temperature to form a slag phase, and the impurities are fully floated by stirring, and the impurities are removed by slagging to improve the purity of the molten steel; silicon iron pre-deoxidation and aluminum wire final deoxidation are used to remove oxygen in the molten steel to avoid the combination of oxygen and alloy elements to form oxide inclusions, which affects the performance of the steel; the cored wire uses low carbon steel strip as the shell, and the rare earth powder is wrapped therein. When feeding into the molten steel, the shell melts first, and the rare earth powder slowly releases in the inert atmosphere (argon stirring environment), avoiding direct exposure to high temperature oxidizing atmosphere, so that the utilization rate of rare earth is improved to more than 80%.

[0025] (3) Casting: bottom pouring ladle casting, pouring temperature 1530-1540 °C, argon blowing in the ladle: 0.3-0.5 m³ / h, heat preservation agent is low carbon graphite and Al2O3;

[0026] (4) Magnetic field assisted targeted heat treatment:

[0027] S1 diffusion annealing: the furnace is cooled to 1020-1050 °C, and the temperature is kept for 3-4 h;

[0028] S2 step quenching:

[0029] Austenitizing: the furnace is cooled to 920-950 °C and kept for 2-2.5 h;

[0030] Bainite transformation: air cooling to 600-650 °C, cooling speed 50-80 °C / s, then mist cooling to 400-450 °C, cooling speed 15-20 °C / s, isothermal at 400-450 °C for 5-10 minutes, while applying low frequency alternating magnetic field;

[0031] Martensite transformation: oil cooling to 150-200 °C, cooling speed 25-30 °C / s;

[0032] S3 low temperature tempering: 200-250 °C for 1.5-2 h, air cooling to room temperature.

[0033] The theoretical basis of diffusion annealing is the principle of solid-state diffusion. At high temperatures, the diffusion rate of alloying elements (such as Cr and Mo) in steel increases, and through holding, the alloying elements can be uniformly distributed, reducing segregation. The austenitizing process is based on the principle of phase transition. The steel is heated to the austenite phase region (920-950°C) to completely austenitize the steel, preparing for subsequent phase transition. The selection of austenitizing temperature is based on the iron-carbon phase diagram and the influence of alloying elements; the bainite transformation process is based on the principle of non-diffusion phase transition. By controlling the cooling rate (air cooling to 600-650°C, fog cooling to 400-450°C), the steel undergoes bainite transformation at 600-650°C, forming lath bainite. The water mist flow and air pressure in the fog cooling stage control the cooling rate at 15-20°C / s to avoid the formation of pearlite and ensure the formation of bainite; the martensite transformation process is based on the principle of non-diffusion phase transition. By oil cooling to 150-200°C, the steel undergoes martensite transformation, forming needle-like martensite. The selection of martensite transformation temperature is based on the critical cooling rate of the steel and the influence of alloying elements; the theoretical basis of low-temperature tempering is the phase transition and stress relaxation principle during tempering. Holding at 200-250°C for 1.5-2 hours can eliminate quenching stress, stabilize the structure, and improve the toughness and wear resistance of the steel. The selection of tempering temperature is based on the tempering stability curve of the steel and the influence of alloying elements.

[0034] Preferably, in the manufacturing method of a semi-autogenous mill wear-resistant alloy dual-phase steel lining plate, the furnace cooling refers to controlling the cooling rate to be 10-15°C / min by fine-tuning the power of the intermediate frequency furnace.

[0035] Preferably, in the manufacturing method of a semi-autogenous mill wear-resistant alloy dual-phase steel lining plate,

[0036] The composite purifying agent in the melting process uses a silicon-aluminum-calcium ternary alloy with an addition amount of 6‰-8‰ of the total weight of the molten steel, forms regular granular bodies with a diameter of 10-50mm through high-pressure forming technology, can form low-melting-point compounds (CaO-Al2O3-SiO2 system) with oxygen and sulfur, and contains silicon ≥20%, aluminum ≥7%, and calcium ≥15%;

[0037] In the ferrosilicon pre-deoxidation, the ferrosilicon addition amount is 0.4%-0.6% of the total weight of the molten steel;

[0038] In the aluminum wire final deoxidation, the aluminum wire addition amount is 0.15%-0.25% of the total weight of the molten steel;

[0039] The rare earth cored wire is formed by wrapping RE with steel sheath, wherein RE is a mixture of La and Ce with a mass ratio of 2:1, and is added into the melting intermediate frequency furnace through wire feeding at a wire feeding speed of 2.5-3m / min; the wire feeding speed (2.5-3m / min) and the molten steel stirring (argon flow rate 1.0-1.2m 3h) Synergistic, rare earth powder is evenly dispersed with the airflow, ensuring that the number of rare earth inclusions in each cubic centimeter of molten steel is ≥10 5

[0040] The Ti-Nb-B composite compression block is obtained by compressing the Ti-Nb-B alloy material according to the addition amount of Ti, Nb and B in the chemical composition of the aforementioned semi-autogenous mill wear-resistant alloy dual-phase steel lining plate, and then drying and heating at >300°C.

[0041] Preferably, in the manufacturing method of the semi-autogenous mill wear-resistant alloy dual-phase steel lining plate, the mass ratio of the low-carbon graphite to the Al2O3 heat insulating agent in the casting (3) is 7:3.

[0042] Preferably, in the manufacturing method of the semi-autogenous mill wear-resistant alloy dual-phase steel lining plate, in the bainite transformation stage of the magnetic field assisted targeted heat treatment (4), the water mist flow rate in the fog cooling stage is 0.5-1.0 L / h, and the air pressure is 0.3-0.5 MPa.

[0043] Air cooling stage (600-650°C, 5-8 seconds): fast cooling speed (about 50-80°C / s), only as a "transition cooling", the purpose is to quickly drop from the austenitizing temperature (920-950°C) to the "preparation temperature zone" (600-650°C) of bainite transformation, to avoid staying in the high temperature zone (>650°C) for too long to cause pearlite nucleation (pearlite nose temperature is about 550°C, and too fast cooling will skip this interval); fog cooling stage (400-450°C, 15-20°C / s): medium and accurately controllable cooling speed, just falls within the critical cooling rate range of bainite transformation - faster than the critical speed of pearlite transformation (<12°C / s) to avoid pearlite generation; and slower than the critical speed of martensite transformation (>25°C / s) to reserve time for bainite nucleation and growth. At the same time, air cooling relies on natural convection of air, and the temperature difference between the surface and the center of the thick piece is small (≤20°C), avoiding local supercooling; fog cooling is through the mixed spraying of water mist and air, with high cooling uniformity.

[0044] Preferably, in the manufacturing method of the semi-autogenous mill wear-resistant alloy dual-phase steel lining plate, in the bainite transformation stage of the magnetic field assisted targeted heat treatment (4), a low-frequency alternating magnetic field is applied, the first 0-3 minutes: 0.4T strong magnetic field, frequency 50-100Hz; the third to tenth minutes: reduced to 0.2T weak magnetic field, frequency 50-100Hz; the magnetic field device used in the magnetic field assisted targeted heat treatment (4) includes: two groups of symmetric Helmholtz coils with an inner diameter of 2-3 times the maximum size of the workpiece and a controller with a frequency of 50-100Hz and capable of outputting a 0.2-0.4T low-frequency alternating magnetic field; each turn of the coil is ≥20 turns, and the material is pure copper.

[0045] ​The low-frequency alternating magnetic field (50-100 Hz) generates a Lorentz force to accelerate the directional migration of charged particles (such as C 4+ 、Fe 2+ ) in steel, which increases the enrichment rate of carbon atoms at the austenite grain boundaries by 30%, forms a "carbon reservoir" at the austenite grain boundaries, and provides sufficient carbon source for the nucleation of bainite, which increases the nucleation density by 40%-50%. The crystal structure of bainite ferrite is body-centered cubic (BCC), which is consistent with ferrite, and its Curie point is close to 770 DEG C, so it has clear ferromagnetism at 400-450 DEG C. The easy magnetization direction of bainite ferrite is consistent with the long axis of the lath, and under the action of a 0.2T magnetic field, the lath spontaneously adjusts the orientation, reduces the intersection and distortion, and the parallel arrangement degree is increased by 5%-10%. At the same time, the magnetic field suppresses the disordered precipitation of carbides between the laths, and promotes the uniform distribution of the carbides along the lath long axis, thereby enhancing the interlath bonding force. Through the stepwise magnetic field intensity (0.4T→0.2T), the precise regulation of "strong magnetic field promoting nucleation-weak magnetic field guiding growth" is realized. Compared with the constant magnetic field, the lath length-diameter ratio is increased, and the problem of "less bainite at the edge and more bainite at the center" in the traditional process is solved, so that the proportion difference of bainite at the center and the edge of the workpiece is ≤±1.5%.

[0046] The beneficial effects of the present application are as follows:

[0047] 1. The present application optimizes the alloy composition by adding appropriate amounts of Cr, Mo, Ti and other elements, and accurately controls the heat treatment process, precisely matches the phase transition window through air cooling and mist cooling, and guarantees the proportion and uniformity of bainite-martensite dual phase; Rare earth cored wire is used to suppress burning loss and promote uniform distribution, maximize the purification and refinement effect of rare earth, and provide high-quality substrate for high-performance organization; Then, through the precise regulation of strong magnetic field promoting nucleation and weak magnetic field guiding growth, the dual-phase structure of 45%-55% lath bainite, 40%-50% acicular martensite and 3%-5% residual austenite is realized, so that the hardness of the liner plate reaches HRC50-55, and the reliability and durability of the liner plate in high stress and high wear environment are ensured.

[0048] 2. By controlling the proportion and characteristics of the bainite+martensite dual-phase structure, the lath bainite is blocked at the lath interface by high-density dislocations, generating a Kossel gas cluster pinning effect; The residual austenite between the laths absorbs crack energy through TRIP effect (transformation induced plasticity); When the load acts, the hard phase martensite (hardness about 580HV) bears the main stress, and the soft phase bainite (hardness about 450HV) coordinates the stress through plastic deformation, and the interface bonding strength is ≥850MPa to ensure effective load transfer. The balance between high strength and good toughness is achieved. At the same time, the impact toughness is good, and the liner plate has excellent crack resistance and impact resistance under complex working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a metallographic structure chart of the dual-phase steel liner prepared in embodiment 2 of the present application under 1000 times magnification;

[0050] Figure 2 is a metallographic structure chart of the dual-phase steel liner prepared in embodiment 2 of the present application under 10000 times magnification;

[0051] Figure 3 is a metallographic structure chart of the alloy steel liner widely used in the current market in comparative example 4 under 1000 times magnification;

[0052] Figure 4 is a metallographic structure chart of the alloy steel liner widely used in the current market in comparative example 4 under 5000 times magnification. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application is further described in detail below with specific examples.

[0054] Example 1:

[0055] Composition (wt%): C: 0.38%, Si: 0.9%, Mn: 1.1%, Cr: 1.9%, Mo: 0.2%, Cu: 0.4%, RE (La:Ce=2:1): 0.25%, Ti: 0.035%, Nb: 0.022%, B: 0.003%, the balance being Fe.

[0056] Preparation steps:

[0057] (1) Molding: V-method molding, using 0.13 mm thick polyethylene film, and the riser neck diameter is 1.4 times the wall thickness of the casting.

[0058] (2) Melting: heating the raw materials to 1670℃ in a medium-frequency furnace, adding CaO-Al2O3-SiO2 composite purifying agent with a total weight of 6.5‰ of the molten steel at 1610℃, stirring for 15 minutes and then removing slag; pre-deoxidizing with 0.45% ferrosilicon and final deoxidizing with 0.18% aluminum wire, controlling the oxygen content to be ≤12 ppm and the sulfur content to be ≤0.008%; stopping heating, cooling to 1530℃ at a rate of 12℃ / min, adding rare earth cored wire (wire feeding speed 2.6 m / min) and Ti-Nb-B composite compression block, and blowing argon for stirring (1.1 m 3 / h) for 11 minutes.

[0059] (3) Casting: bottom pouring package casting, pouring temperature 1535℃, argon blowing in the package 0.4 m 3 / h, and the heat preservation agent is low-carbon graphite and Al2O3 (mass ratio 7:3).

[0060] (4) Magnetic field assisted targeted heat treatment:

[0061] S1 diffusion annealing: cooling down to 1030 °C at 12 °C / min, holding for 3.2 h;

[0062] S2 step quenching: austenitizing at 930 °C for 2.2 h, air cooling to 620 °C (6 s), then mist cooling to 420 °C (water mist flow rate 0.6 L / h, air pressure 0.35 MPa, cooling rate 16 °C / s), isothermal at 420 °C for 7 min (0.4 T / 60 Hz for the first 3 min, 0.2 T / 60 Hz for the last 4 min), oil cooling to 170 °C (cooling rate 27 °C / s);

[0063] S3 low-temperature tempering: holding at 220 °C for 1.6 h, air cooling to room temperature.

[0064] Example 2:

[0065] Composition (wt%): C: 0.42%, Si: 1.0%, Mn: 1.3%, Cr: 2.2%, Mo: 0.4%, Cu: 0.5%, RE (La:Ce=2:1): 0.3%, Ti: 0.04%, Nb: 0.025%, B: 0.004%, balance Fe.

[0066] Preparation steps:

[0067] (1) Molding: V-process molding, using 0.14 mm thick polyethylene film, the riser neck diameter is 1.5 times the wall thickness of the casting.

[0068] (2) Melting: heating the raw materials to 1670 °C in a medium-frequency furnace, adding CaO-Al2O3-SiO2 composite purifying agent at a total weight of 7‰ of the steel liquid at 1610 °C, stirring for 15 min, then skimming the slag; pre-deoxidizing with 0.5% ferrosilicon and final deoxidizing with 0.2% aluminum wire, controlling the oxygen content to be ≤12 ppm and the sulfur content to be ≤0.008%; stopping heating, cooling down to 1535 °C at 13 °C / min, adding rare earth cored wire (wire feeding speed 2.8 m / min) and Ti-Nb-B composite compact, argon blowing and stirring (1.1 m 3 / h) for 12 min.

[0069] (3) Casting: bottom pouring package casting, pouring temperature 1535 °C, argon blowing in the package 0.4 m 3 / h, heat preservation agent is low-carbon graphite and Al2O3 (mass ratio 7:3).

[0070] (4) Magnetic field assisted targeted heat treatment:

[0071] S1 diffusion annealing: cooling down to 1035 °C at 13 °C / min, holding for 3.5 h;

[0072] S2 partition quenching: austenitizing at 935℃ for 2.3h with 13℃ / min cooling rate, air cooling to 630℃ (7s), then mist cooling to 430℃ (water mist flow rate 0.7L / h, air pressure 0.4MPa, cooling rate 18℃ / s), isothermal at 430℃ for 8min (0.4T / 80Hz for the first 3min, 0.2T / 80Hz for the last 5min), oil cooling to 180℃ (cooling rate 28℃ / s);

[0073] S3 low temperature tempering: 230℃ for 1.7h, air cooling to room temperature.

[0074] The metallographic structure of the dual-phase steel liner prepared in Example 2 at different multiples is shown in FIG. 1, which shows a uniform distribution of lath-shaped bainite and acicular martensite dual-phase structure. Figure 1

[0075] Example 3:

[0076] Composition (wt%): C: 0.48%, Si: 1.1%, Mn: 1.4%, Cr: 2.4%, Mo: 0.6%, Cu: 0.5%, RE (La:Ce=2:1): 0.35%, Ti: 0.045%, Nb: 0.028%, B: 0.004%, and the balance of Fe.

[0077] Preparation steps:

[0078] (1) Molding: V-process molding, 0.14mm thick polyethylene film covering, and the riser neck diameter is 1.5 times the wall thickness of the casting.

[0079] (2) Melting: heating the raw materials to 1680℃ in a medium-frequency furnace, adding CaO-Al2O3-SiO2 composite purifying agent accounting for 7.5‰ of the total weight of the molten steel at 1620℃, stirring for 15min, and then skimming; pre-deoxidizing with 0.55% ferrosilicon and final deoxidizing with 0.22% aluminum wire, controlling the oxygen content to be ≤12ppm and the sulfur content to be ≤0.008%; stopping heating, cooling to 1540℃ at a rate of 14℃ / min, adding rare earth cored wire (wire feeding speed 2.9m / min) and Ti-Nb-B composite compression block, and argon blowing and stirring (1.15m 3 / h) for 12min.

[0080] (3) Casting: bottom pouring package casting, pouring temperature 1538℃, argon blowing in the package 0.45m 3 / h, and the heat preservation agent is low-carbon graphite and Al2O3 (mass ratio 7:3).

[0081] (4) Magnetic field assisted targeted heat treatment:

[0082] S1 diffusion annealing: cooling to 1040℃ at a rate of 14℃ / min, and holding for 3.8h; ​

[0083] S2 partition quenching: cooling at 14℃ / min to 940℃ for 2.4h austenitizing; air cooling to 640℃ (7s), then mist cooling to 440℃ (water mist flow rate 0.9L / h, air pressure 0.45MPa, cooling rate 19℃ / s), 440℃ isothermal for 9min (0.4T / 90Hz for the first 3min, 0.2T / 90Hz for the last 6min); oil cooling to 190℃ (cooling rate 29℃ / s);

[0084] S3 low temperature tempering: 240℃ for 1.9h, air cooling to room temperature.

[0085] Comparative Example 1:

[0086] The composition is the same as that of Example 2, except that no low-frequency alternating magnetic field is applied during the bainite transformation stage, and the rest of the preparation steps are consistent.

[0087] Comparative Example 2:

[0088] The composition is the same as that of Example 2, and during smelting, the rare earth core wire is replaced by an equal amount of block-shaped rare earth directly added, and the rest of the preparation steps are consistent.

[0089] Comparative Example 3:

[0090] The composition is the same as that of Example 2, and the cooling method during the bainite transformation stage is changed to "oil cooling to 620℃→water cooling to 430℃", and the rest of the preparation steps are consistent.

[0091] Comparative Example 4:

[0092] It is an alloy steel liner plate widely used in today's market. Its surface metallography is shown in FIGS. 1 and 2, and its metallographic structure is pearlite + tempered sorbite. Figure 3 and Figure 4

[0093] Performance test:

[0094] 1. Bainite / martensite ratio, aspect ratio and arrangement degree

[0095] Test method: observed by optical microscope (OM) and scanning electron microscope (SEM, model such as ZEISS Sigma300).

[0096] Steps:

[0097] Take a sample size of 10mm×10mm×5mm, polish it, and then etch it with 4% nitric acid alcohol solution;

[0098] The area ratio of each phase (bainite / martensite / residual austenite) is counted by Image-ProPlus image analysis software;

[0099] ​Measure the long axis and short axis size of more than 50 bainite laths, and calculate the aspect ratio;

[0100] Calculate the parallel arrangement degree (the proportion of laths with an angle ≤ 15°) by counting the angle between the lath axis and the magnetic field direction.

[0101] 2. Retained Austenite Content

[0102] Test method: X-ray diffractometer (XRD, such as Bruker D8 Advance), using Cu-Kα target, scanning range 40°-100°.

[0103] Principle: Calculate the volume fraction of retained austenite by the ratio of the diffraction peak intensity of austenite (200), (220), (311) crystal faces to the intensity of ferrite / martensite (200), (211) peaks, combined with Rietveld full spectrum fitting.

[0104] 3. Hardness (HRC)

[0105] Test method: Rockwell hardness tester (such as HR-150A), according to GB / T230.1-2018 standard.

[0106] Steps: Uniformly select 5 points on the surface of the sample (avoiding the edge 2mm), load 150kgf main load, and take the average value.

[0107] 4. Tensile Strength and Elongation

[0108] Test method: Universal material testing machine (such as Instron 5982), according to GB / T228.1-2010 standard.

[0109] Sample: Prepare Φ10mm×50mm round tensile sample (gauge length section 30mm);

[0110] Steps: Load rate 2mm / min, record the maximum load at break (calculate tensile strength) and gauge length elongation (calculate elongation).

[0111] 5. Impact Toughness (U-notch / No-notch)

[0112] Test method: Pendulum impact tester (such as ZBC 2452), according to GB / T229-2020 standard.

[0113] Sample: U-notch sample size 10mm×10mm×55mm (notch depth 2mm, radius 1mm), no-notch sample size is the same;

[0114] Steps: Test after 30 minutes of insulation at -20℃, record the impact absorbed work (average value of 3 samples).

[0115] 6. Interface bonding strength

[0116] Test method: Tensile shear test (refer to GB / T6396-2008).

[0117] Sample preparation: Prepare a bainite-martensite interface shear sample (overlap area 10mm×10mm).

[0118] Steps: Apply shear load using a universal testing machine, record the maximum load during interface separation, and calculate the strength per unit area.

[0119] 7. Machine service life (days)

[0120] Three liners of the same specification (three for the example and three for the comparative example) were installed in the same compartment of the mill to ensure consistent operating conditions (stable speed, ore flow, etc.). The mill was shut down for inspection every 7 days, and the remaining thickness, weight loss, and damage were recorded. The failure criteria were defined as "remaining thickness reaching 50% of the initial thickness" or "the appearance of critical cracks / sparging," and the cumulative operating time was converted to days (based on actual operating procedures). The average value of the three liners was taken, and the lifespan differences between the groups were compared to verify durability.

[0121] The test results are shown in Table 1.

[0122] Table 1 Performance test results of embodiments and comparative examples of the present invention

[0123]

[0124] Data Analysis:

[0125] 1. Comparing Example 2 with Comparative Example 1, the key role of magnetic field assistance can be observed:

[0126] Microstructure control: After applying a magnetic field, the aspect ratio of bainite increased from 12:1 to 16:1, and the parallel alignment increased from 72% to 88%. This indicates that the magnetic field achieved directional optimization of bainite through "strong magnetic field promoting nucleation + weak magnetic field guiding growth," solving the problem of disordered bainite arrangement in traditional processes. Figure 1 and Figure 2 As shown;

[0127] Performance improvements: Tensile strength increased from 1450MPa to 1525MPa, and U-notch impact energy increased from 20J / cm². 2 Increased to 32J / cm 2 The interfacial bonding strength increased from 780 MPa to 860 MPa. The core reason is that the magnetic field-induced directional arrangement of bainite enhanced the tissue's ability to withstand stress and suppressed the disordered precipitation of carbides.

[0128] 2. Comparing Example 2 with Comparative Example 2, the advantages of rare earth cored wires can be observed:

[0129] Tissue uniformity: When using cored wire feeding, the bainite arrangement degree is increased from 75% to 88%, avoiding local segregation caused by blocky rare earth, such as the rare earth enrichment area in Comparative Example 2, while Example 2 reduces rare earth burning due to the isolation protection of the cored wire, and the utilization rate is increased from 50% to 80%, achieving uniform distribution.

[0130] Toughness improvement: The unnotched impact energy is increased from 200 J / cm 2 to 260 J / cm 2 , which confirms that rare earth purifies the grain boundary by reducing oxygen and sulfur content, refining austenite grains from 50 μm to 30 μm, achieving grain refinement and improving toughness.

[0131] 3. Comparative Example 2 and Comparative Example 3 can obtain the value of precise temperature control of air cooling + fog cooling:

[0132] Phase transition window matching: Air cooling + fog cooling increases the bainite proportion from 42% to 52%, while the oil cooling + water cooling of Comparative Example 3 causes cooling rate fluctuation, exceeding the bainite critical range, resulting in a high proportion of martensite, more than 55%, which shows that the air cooling + fog cooling of Example 2 can stably control the cooling rate of 15-20 ℃ / s, and precisely fall into the bainite transformation interval.

[0133] Stress control: Comparative Example 3 reduces elongation to 2.9% due to severe cooling, and micro-cracks appear, while the slow cooling + precise fog cooling of Example 2 reduces thermal stress, ensuring that the elongation is maintained at 3.6%, verifying the guarantee effect of this cooling method on the uniformity of thick pieces (60-80 mm).

[0134] 4. Parameter coordination law among examples

[0135] Component and performance balance: The toughness of the product of Example 1 with low C and low alloy is slightly better, with an elongation of 3.6%; the product of Example 3 with high C and high alloy has a higher hardness, HRC 54; which shows that the composition can be fine-tuned according to the working condition requirements within the limited range, and all can meet the core indicators of HRC 50-54 and tensile strength ≥1520 MPa.

[0136] Process stability: The bainite proportion of the three examples is 48%-54%, and the residual austenite is 3%-5%, all within the target range, and the difference between the core and the corner is ≤±1.5%, proving the stability and repeatability of process parameters such as magnetic field frequency and fog cooling rate.

[0137] The present application realizes the precise matching of "composition-technology-tissue-performance" through the synergistic design of magnetic field assistance + rare earth cored wire + air cooling and fog cooling: the core performance all reaches the target interval (hardness HRC 50-54, tensile strength 1520-1530 MPa, impact energy 26-36 J / cm2 );compared with Comparative Example 1-4, the key performance indicators are improved by 10%-60%, especially in toughness and interface bonding strength, which fully meets the use requirements of semi-autogenous mill liner under high stress and high wear conditions. Its comprehensive performance is much higher than that of the alloy steel liner plate wear-resistant steel widely used in the market today. Through on-site use, its service life is increased from 95 days to more than 154 days, an increase of more than 60%. The liner plate has higher wear resistance, longer service life, and better grinding efficiency, and its market benefit is considerable.

[0138] It should be understood by those of ordinary skill in the art that the above discussion of any of the embodiments is only exemplary and is not intended to imply that the scope of the application is limited to these examples; under the idea of the present application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail.

Claims

1. A duplex steel liner plate for a semi-autogenous mill, characterized by, The chemical composition includes, by mass percentage, C: 0.35%-0.5%, Si: 0.8%-1.2%, Mn: 0.2%-0.6%, Cr: 1.8%-2.5%, Mo: 0.2%-0.6%, Cu: 0.3%-0.6%, RE: 0.2%-0.4%, Ti: 0.03%-0.05%, Nb: 0.02%-0.03%, B: 0.002%-0.005%, and the balance of Fe and inevitable impurities; The microstructure of the double-phase wear-resistant alloy lining plate for the semi-autogenous mill comprises 45%-55% lath bainite, 40%-50% acicular martensite and 3%-5% residual austenite; the lath bainite has a length-diameter ratio of greater than or equal to 15:1 and a parallel arrangement degree of greater than or equal to 85%.

2. The method of manufacturing a duplex wear-resistant alloy steel liner plate for a semi-autogenous mill according to claim 1, characterized in that, The method comprises the following steps: (1) molding: V-process molding technology is adopted, 0.12-0.15 mm thick polyethylene film is used, and a hot riser is used for feeding, and the riser neck diameter is 1.3-1.6 times of the wall thickness of the casting; (2) Smelting: the intermediate frequency furnace is heated to 1660-1680 °C, and pig iron, scrap steel and alloying materials are added to melt; 1600-1620 °C, add composite purifying agent; then use silicon iron pre-deoxidation and aluminum wire final deoxidation, stir for 15 minutes, then remove slag, control oxygen content ≤12 ppm, control sulfur content ≤0.008%; then stop heating, the furnace is cooled to 1520-1550 °C, add rare earth cored wire and Ti-Nb-B composite compression block, argon blowing stirring: 1.0-1.2 m 3 / h, ≥10 minutes; (3) Casting: bottom pouring ladle casting, pouring temperature 1530-1540 °C, argon blowing in ladle: 0.3-0.5 m 3 / h, holding agent is low-carbon graphite and AI2O3; (4) magnetic field assisted targeted heat treatment: S1 diffusion annealing: furnace cooling to 1020-1050℃, holding for 3-4h; S2 staged quenching: austenitizing: furnace cooling to 920-950℃, holding for 2-2.5h; bainite transformation: air cooling to 600-650℃ at a cooling rate of 50-80℃ / s, then fog cooling to 400-450℃ at a cooling rate of 15-20℃ / s, and isothermal holding for 5-10min at 400-450℃ while a low-frequency alternating magnetic field is applied; martensite transformation: oil cooling to 150-200℃ at a cooling rate of 25-30℃ / s; S3 low-temperature tempering: holding for 1.5-2h at 200-250℃, and air cooling to room temperature.

3. The method of manufacturing a duplex steel liner plate for a semi-autogenous mill according to claim 2, wherein The furnace cooling refers to adjusting the power of the medium-frequency furnace to control the cooling rate to be 10-15℃ / min.

4. The method of manufacturing a dual phase steel liner plate for a semi-autogenous mill according to claim 2, wherein In the (2) melting, a silicon-aluminum-calcium ternary alloy is used as a composite purifying agent, and the adding amount is 6‰-8‰ of the total weight of the molten steel, and the regular granular body with a diameter of 10-50mm is formed by high-pressure forming technology, wherein the silicon is greater than or equal to 20%, the aluminum is greater than or equal to 7%, and the calcium is greater than or equal to 15%; In the silicon-iron pre-deoxidation, the adding amount of the silicon-iron is 0.4%-0.6% of the total weight of the molten steel; In the aluminum wire final deoxidation, the adding amount of the aluminum wire is 0.15%-0.25% of the total weight of the molten steel; The rare earth cored wire is formed by wrapping RE with steel skin, wherein the RE is a mixture of La:Ce in a mass ratio of 2:1, and is added into the melting medium-frequency furnace by wire feeding at a wire feeding speed of 2.5-3m / min; The Ti-Nb-B composite compression block is obtained by compressing Ti-Nb-B alloy materials according to the adding amounts of Ti, Nb and B in the chemical composition in claim 1, and then drying treatment at >300℃.

5. The method of manufacturing a dual phase steel liner plate for a semi-autogenous mill according to claim 2, wherein In the (3) casting, the mass ratio of low-carbon graphite to Al2O3 heat preservation agent is 7:

3.

6. The method of manufacturing a dual phase steel liner plate for a semi-autogenous mill according to claim 2, wherein In the bainite transformation stage of the (4) magnetic field assisted targeted heat treatment, the water mist flow rate is 0.5-1.0L / h, and the air pressure is 0.3-0.5MPa.

7. The method of manufacturing a dual phase steel liner plate for a semi-autogenous mill according to claim 2, wherein The low-frequency alternating magnetic field is applied in the bainite transformation stage in the magnetic field assisted targeted heat treatment, and the magnetic field is 0.4T strong magnetic field with a frequency of 50-100Hz in the first 0-3 minutes, and is 0.2T weak magnetic field with a frequency of 50-100Hz in the 3rd-10th minute; the magnetic field device used in the magnetic field assisted targeted heat treatment comprises two groups of symmetrical Helmholtz coils with an inner diameter of 2-3 times of the maximum size of the workpiece and a controller with a frequency of 50-100Hz and capable of outputting a low-frequency alternating magnetic field of 0.2-0.4T; each turn of the coil is greater than or equal to 20 turns, and the material of the coil is pure copper.

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